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bees: fix deadlock in thread status reporting

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"s_name" was a thread_local variable, not static, and did not require a
mutex to protect access.  A deadlock is possible if a thread triggers an
exception with a handler that attempts to log a message (as the top-level
exception handler in bees does).

Remove multiple unnecessary mutex locks.  Rename the thread_local variables
to make their scope clearer.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell 2017-01-15 00:30:00 -05:00
parent 382f8bf06a
commit 9f120e326b
2 changed files with 22 additions and 23 deletions
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37
src/bees.cc
View File

@ -46,7 +46,7 @@ do_cmd_help(const char **argv)
RateLimiter bees_info_rate_limit(BEES_INFO_RATE, BEES_INFO_BURST); RateLimiter bees_info_rate_limit(BEES_INFO_RATE, BEES_INFO_BURST);
thread_local BeesTracer *BeesTracer::s_next_tracer = nullptr; thread_local BeesTracer *BeesTracer::tl_next_tracer = nullptr;
BeesTracer::~BeesTracer() BeesTracer::~BeesTracer()
{ {
@ -56,20 +56,20 @@ BeesTracer::~BeesTracer()
BEESLOG("--- END TRACE --- exception ---"); BEESLOG("--- END TRACE --- exception ---");
} }
} }
s_next_tracer = m_next_tracer; tl_next_tracer = m_next_tracer;
} }
BeesTracer::BeesTracer(function<void()> f) : BeesTracer::BeesTracer(function<void()> f) :
m_func(f) m_func(f)
{ {
m_next_tracer = s_next_tracer; m_next_tracer = tl_next_tracer;
s_next_tracer = this; tl_next_tracer = this;
} }
void void
BeesTracer::trace_now() BeesTracer::trace_now()
{ {
BeesTracer *tp = s_next_tracer; BeesTracer *tp = tl_next_tracer;
BEESLOG("--- BEGIN TRACE ---"); BEESLOG("--- BEGIN TRACE ---");
while (tp) { while (tp) {
tp->m_func(); tp->m_func();
@ -78,18 +78,19 @@ BeesTracer::trace_now()
BEESLOG("--- END TRACE ---"); BEESLOG("--- END TRACE ---");
} }
thread_local BeesNote *BeesNote::s_next = nullptr; thread_local BeesNote *BeesNote::tl_next = nullptr;
mutex BeesNote::s_mutex; mutex BeesNote::s_mutex;
map<pid_t, BeesNote*> BeesNote::s_status; map<pid_t, BeesNote*> BeesNote::s_status;
thread_local string BeesNote::s_name; thread_local string BeesNote::tl_name;
BeesNote::~BeesNote() BeesNote::~BeesNote()
{ {
tl_next = m_prev;
if (tl_next) {
unique_lock<mutex> lock(s_mutex); unique_lock<mutex> lock(s_mutex);
s_next = m_prev; s_status[gettid()] = tl_next;
if (s_next) {
s_status[gettid()] = s_next;
} else { } else {
unique_lock<mutex> lock(s_mutex);
s_status.erase(gettid()); s_status.erase(gettid());
} }
} }
@ -97,28 +98,26 @@ BeesNote::~BeesNote()
BeesNote::BeesNote(function<void(ostream &os)> f) : BeesNote::BeesNote(function<void(ostream &os)> f) :
m_func(f) m_func(f)
{ {
m_name = tl_name;
m_prev = tl_next;
tl_next = this;
unique_lock<mutex> lock(s_mutex); unique_lock<mutex> lock(s_mutex);
m_name = s_name; s_status[gettid()] = tl_next;
m_prev = s_next;
s_next = this;
s_status[gettid()] = s_next;
} }
void void
BeesNote::set_name(const string &name) BeesNote::set_name(const string &name)
{ {
unique_lock<mutex> lock(s_mutex); tl_name = name;
s_name = name;
} }
string string
BeesNote::get_name() BeesNote::get_name()
{ {
unique_lock<mutex> lock(s_mutex); if (tl_name.empty()) {
if (s_name.empty()) {
return "bees"; return "bees";
} else { } else {
return s_name; return tl_name;
} }
} }

6
src/bees.h
View File

@ -184,7 +184,7 @@ class BeesTracer {
function<void()> m_func; function<void()> m_func;
BeesTracer *m_next_tracer = 0; BeesTracer *m_next_tracer = 0;
thread_local static BeesTracer *s_next_tracer; thread_local static BeesTracer *tl_next_tracer;
public: public:
BeesTracer(function<void()> f); BeesTracer(function<void()> f);
~BeesTracer(); ~BeesTracer();
@ -200,8 +200,8 @@ class BeesNote {
static mutex s_mutex; static mutex s_mutex;
static map<pid_t, BeesNote*> s_status; static map<pid_t, BeesNote*> s_status;
thread_local static BeesNote *s_next; thread_local static BeesNote *tl_next;
thread_local static string s_name; thread_local static string tl_name;
public: public:
BeesNote(function<void(ostream &)> f); BeesNote(function<void(ostream &)> f);